Washington — The US government maintains a multi-level system of watch lists to try and identify possible terrorists before they enter the country.

These lists have come under intense scrutiny in the wake of the failed attempt to blow up an airliner bound for Detroit on Christmas Day. The system contained the name of the alleged bomber in the case, Umar Farouk Abdulmutallab. Yet he yet still managed to fly from Nigeria, through Amsterdam, to the US.

According to an NCC fact sheet, the sorts of activity that can get on included in TIDE are everything from possible terrorist activity to the provision of material support for terrorists, such as safe houses, communications, or money.

The Terrorist Watchlist

Every evening, some of the names added that day to the TIDE list get sent over to the FBI’s Terrorist Screening Center for possible inclusion in the second level Terrorist Watchlist, which contains approximately 400,000 names.

To make this list, a name must meet two requirements, according to Timothy Healy, director of the Terrorist Screening Center (TSC). First, there must be enough biographical information attached to the name to allow investigators to make sure they are dealing with the right person. Second, that information must establish that there is a reasonable suspicion that the person in question has engaged, or might engage, in terrorist activity.

“Due weight must be given to the reasonable inferences that a person can draw from the facts. Mere guesses or inarticulate ‘hunches’ are not enough to constitute reasonable suspicion,” said Mr. Healy in written testimony submitted to the Senate Homeland Security and Governmental Affairs Committee prior to a December 9 hearing.

Abdulmutallab apparently had been flagged for inclusion in this second-level list. But prior to his takeoff from Amsterdam, he had not been added to a third and far shorter list: the no-fly database.

The no-fly list

The no-fly list has its own minimum criteria, according to the FBI’s Healy. To be included, one must be a known or suspected terrorist thought to present an imminent threat to civil aviation or US national security.

There are some 3,400 people on the TSC’s no-fly list. Most are foreigners. About 170 are US citizens.

Names are continually added and subtracted from all these lists. Every day, the TSC handles between 400 and 1,200 additions, modifications, or deletions of terrorist identities, according to Healy.